Water soluble film



3,086,900 WATER SULUBLE FliLM Milton F. Fillius and .larnes S. Bruce, Rochester, N.Y.,

assignors to the United States of America as represented by the Secretary of the Navy N Drawing. Filed Jan. 29, 1945, Ser. No. 575,198 1 Claim. (Cl. 156-155) This invention is concerned with the provision of a water soluble film bearing a silver image, and it relates more particularly to microfilm of this character.

Microfilm of the conventional cellulose ester variety is at present employed as the medium of transmittal of various messages, including those of a secret character. When the film is used in the transmission of the latter type message, it sometimes becomes necessary to effect rapid destruction of the film so as to prevent its falling into enemy hands. However, cellulose ester films are not soluble in water, and accordingly, the need has been felt to supply microfilm which could be readily destroyed by the placing thereof in the mouth or in other available aqueous media.

It is therefore an object of our invention to provide 13. water soluble film bearing a silver image thereon. Another object is to provide a method of obtaining such an image-bearing, water soluble film, and particularly a microfilm of this character.

We have discovered that these objects may be attained through utilization of a film composed essentially of hydroxyethyl cellulose, and preferably containing a plasticizing ingredient such as glycerine. This film, either with or Without the plasticizing ingredient, is known 'as H.E.C. film. The principle of our invention involves the transfer to the surface of the H.E.C. film, and the afiixing thereto, of the gelatin emulsion from a conventional cellulose ester film base. The gelatin emulsion so transferred incorporates a silver image.

The method of obtaining the water soluble film base will now be described in detail. The H.E.C., or water soluble, film which is here utilized may be prepared by flowing a water solution of hydroxyethyl cellulose over a flat, smooth surface such as that of glass and allowing the material to dry thereon. This material is available commercially :as a water solution containing about percent by weight hydroxyethyl cellulose. As stated above, in the preferred practice of our invention, We also incorporate in the solution a plasticizing ingredient such as glycerine; while the amount of plasticizer used may be varied within Wide limits, particularly good results have been obtained by using about 10 percent by weight glycerine in the hydroxyethyl cellulose solution. After this solution has been placed on the flat smooth surface and allowed to dry, the H.E.C. film may then be stripped away. The thickness of the film formed in this manner is dependent on the viscosity and solid content of the w er olu ion u ed.

Patented Apr. 23, 1963 3 ICQ Once the H.E.C. film is obtained, the gelatin emulsion is transferred to it from a conventional film base such as cellulose nitrate or cellulose acetate. The following example will serve to illustrate the processes by which the transfer is elfected.

Example A cellulose nitrate base microfilm, bearing on its surface a gelatin emulsion incorporating a silver image, was prepared and processed in the normal fashion. It was then soaked in warm water, preferably maintained at a temperature of about F., for a period of about one hour. A previously prepared H.E.C. film was then placed on a glass surface, and a laminated structure was formed by placing the wet cellulose nitrate film, gelatin side downward, on the H.E.C. film. This lamination step Was completed by using a roller to press all portions of the cellulose nitrate film into fir-m engagement with the H.E.C. film. The resulting laminated film was then dried, after which it was placed in an acetone bath and kept therein for a period of about one-half hour. The acetone bath was constantly agitated during the time the film was under treatment therein. At the end of this immersion period, the cellulose nitrate backing was found to be completely removed, and dissolved in the bath. However, the treatment did not affect the H.E.C. film. nor did it affect the gelatin emulsion or the silver image included therein. Upon further drying to remove the acetone, the H.E.C. film, with the adhering gelatin emulsion and its silver image, was ready for use. It was found to be readily destru ctible by being placed in the mouth or in other water solution, where, within a few seconds, it became a gummy, sticky mass.

What is claimed is:

The method of preparing a water soluble film comprising preparing and processing a cellulose ester film base bearing on its surface a gelatin emulsion and containing a silver image in said emulsion; soaking said cellulose ester film in warm Water; laminating said wet cellulose ester film against a film base comprising hydroxyethyl cellulose, the said gelatin emulsion being placed against said hydroxyethyl cellulose film base; drying said laminated film; dissolving the cellulose ester component of said laminated film in an acetone bath; and drying said hydroxyethyl cellulose film and the adhering gelatin emulsion after removal from said acetone bath.

References (Iited in the file of this patent UNITED STATES PATENTS 409,507 Schwalz Aug. 20, 1889 1,396,409 De Rooij Nov. 8, 1921 1,939,171 Hichman Dec. 12, 1933 2,214,205 Potter Sept. 10, 1940 2,216,736 Carothers Oct. 8, 1940 2,274,706 Kein Mar. 3, 1942 2,357,590 Jtaife Sept. 5, 1944 2,391,867 Clark Ian. 1, 1946 

